1. Field of the Invention.
The present invention relates to the manufacture of thin film magnetic read write heads. In particular, the invention relates to the use of a positively sloped top pole to facilitate an ion milling alignment process.
2. Description of the Prior Art.
The quest for increased data storage density has continually driven data storage technology. Thin film magnetic read/write heads have greatly increased the magnitude of data storage density obtainable in a magnetic storage medium. This increase has been largely due to the small size of thin film magnetic heads.
In a thin film magnetic head, a gap area is formed at the tips of two legs or pole pieces used to form the flux path of the thin film head. This flux path is closed at the end opposite the gap area by a backgap via. Conductors carry electric current through the center of the thin film head and between the two magnetic legs. When an electric current flows through these conductors, a magnetic flux is caused to flow in the core (i.e. the two leg pieces) of the thin film head. During operation, magnetic fields may be impressed upon a magnetic storage medium by this magnetic flux. As the flux spans the gap area, a magnetic fringe field emanates from the pole tips. Conversely, information may be recovered from a magnetic storage medium, because a varying magnetic field near the gap area induces an electrical current to flow in the conductors.
One area in which thin film head performance may be enhanced is in the alignment between upper and lower pole tips. This alignment is critical because it defines the characteristic fringe field. The magnetic field density and gradient are directly related to this alignment.
A technique which provides better pole tip alignment begins with a bottom pole deposited upon a substrate, in which the bottom pole is substantially wider than desired. Next an insulator is deposited upon the bottom pole and forms the gap area in the completed pole tip. A top pole is deposited upon the insulator. The top pole is deposited by using a photoresist process comprising: depositing a photoresist layer; exposing the photoresist layer to radiation; and applying a photoresist developer which chemically develops out (i.e. removes or "etches") out a three dimensional relief in the layer. The top pole piece is deposited upon the insulator and formed using a conventional positive photoresist with a "positively sloped profile." A positively sloped profile is a profile which is wider at the top or outer edge than at bottom, inner edge closest to the substrate. The resulting top pole formed by the positive tone photoresist has a profile with negatively sloped sides.
A protective photoresist layer may then be deposited upon the top pole. The protective photoresist layer comprises positive photoresist having a positive tone with a positively sloped profile. The nonaligned pole tip structure is aligned using a material removal process such as ion milling. In ion milling, high energy ions bombard the surface to remove the nonaligned portions of the pole tip. The protective photoresist mask shields the top pole and a portion of the insulating gap material and bottom pole from the high energy ions. This leaves behind a substantially aligned pole tip structure.
There are a number of problems associated with this alignment technique. The protective photoresist mask and the top pole have profiles with opposing slopes. This causes a lip to be formed at their intersection. This lip provides an area for redeposition of milled material during the ion milling process. The self masking of the top pole during ion milling limits the accuracy of the ultimate pole tip width.